Cutworms

Multiple Species

Appearance and Life History

Dingy CutwormPhoto by B. Christine

Cutworms can attack crops virtually anywhere in the Midwest. The importance of a particular species of cutworm varies with how and when it damages corn. Some species feed much like the black cutworm and can cause extensive crop damage, others are more like armyworms that climb the plant to feed on foliage. Often an infested field will have a mixed population of several species of cutworms. Because they vary in their feeding habits, early diagnosis of cutworm infestations are essential.

Variegated cutwormPhoto by Purdue University

The bodies of cutworms are cylindrical and may vary in length from 1/8 to 1-1/2 inches (3.2 to 38.1 mm), depending on the species. Often, 3 or 4 different sizes of cutworm will be noted in a typical field collection. Cutworms may lack any visible markings or may be distinctly marked with spots or stripes. Color may range from black, gray, and brown to nearly white or translucent.

Claybacked cutwormPhoto by J. Obermeyer

Most cutworms overwinter as pupae in the soil or as young larvae. After mating, moths deposit eggs on soil, weeds, and/or cultivated plants, if present. Feeding begins in the spring. This may occur before or after planting.

The larvae hatch in 2 days to 2 weeks, molt several times and mature in 2 weeks to 5 months. Most cutworms have one generation per year, while some species have 2 to 4.

Damage

Sandy knoll with sandhill cutworm damagePhoto by Purdue University

Early cutworm feeding may include holes chewed in leaves. Leaf margins may appear ragged. This above ground injury occurs early in the cutworm's developmental stages. At this time, young worms feed above ground at night or on cloudy days. Older larger worms often cut plants at or below ground level. Cutworms often pull cut plants into their burrows to feed on at their leisure. Larger worms tend to remain below the soil surface, especially if the weather is dry and a surface crust has formed.

Sampling Method

Cutworms remain hidden in the soil or under crop residue during the day. To find them, examine the top several inches of soil or under plant residues around damaged plants. If most residue is between the rows, the cutworms may be found there instead. Since the color of some cutworms blends with the soil, they may be easily overlooked.

To monitor for cutworm damage, walk fields as plants emerge. Randomly check 20 plants in each of 5 areas of a field (100 total plants). Record the number of cut or damaged plants for each area and the field as a whole. Make a note of leaf feeding that may be due to young cutworms. Record the average number of fully unrolled leaves for the field. Check fields again in 24 to 48 hours. Be sure to monitor those areas of the field where cutworms are most likely to be found (wet, weedy areas).

Also, look for live cutworms around damaged plants. Collect 2 cutworms from each sample set for a total of 10 and record the body length of each. Determine the average length and species of cutworm causing the damage.